1. Field of the Invention
The present invention relates to a magnetoresistive effect element (MR element) in a current perpendicular to plane (CPP) type structure that detects magnetic field intensity as a signal from a magnetic recording medium, and so on, a thin film magnetic head with the MR element, and a head gimbal assembly and a magnetic disk device that have the thin film magnetic head.
2. Description of Related Art
In recent years, with an increase in the high recording density of a magnetic disk drive (HDD), there have been growing demands for improvements in the performance of a thin film magnetic head. For a thin film magnetic head, a composite type thin film magnetic head has been widely used; it has a structure where a reproducing head having a read-only magnetoresistive effect element (hereinafter, magneto-resistive (MR) element), and a recording head having a write-only induction type magnetic conversion element are laminated together.
Generally, a shield layer is formed in a reproducing head to restrict an area of a medium that interferes with a reproducing element. Currently, in a conventional head structure, a first shield film, a second shield film and an MR element are connected in series without an intershield insulating layer. This structure is referred to as an MR element in a CPP-type structure. In consideration of the efficiency of heat dissipation and maintenance of an output, and so on, a CPP-type structure is essential to realize a high recording density beyond 500 Gbits/in2.
A general CPP-type element with a spin valve is briefly explained below. A typical spin valve CPP-type element is formed by a lamination structure for its main layers as follows: a lower electrode layer/an under layer/an antiferromagnetic layer/a ferromagnetic layer (1)/a spacer layer/a ferromagnetic layer (2)/a cap layer/an upper electrode layer. The top most layer is the upper electrode layer, and the bottom most layer is the lower electrode layer. In the specification hereinafter, a lamination structure may be described as having the above format.
A magnetization direction of the ferromagnetic layer (1), which is one of the ferromagnetic layers, is pinned in the perpendicular direction to a magnetization direction of the ferromagnetic layer (2) when an externally applied magnetic field is zero. The ferromagnetic layer (2) is generally referred to as a magnetic free layer. The magnetization direction of the ferromagnetic layer (1) can be pinned by making an antiferromagnetic layer adjacent thereto and providing unidirectional anisotropic energy (also referred to as “exchange bias” or “coupling magnetic field”) to the ferromagnetic layer (1) by means of exchange-coupling between the antiferromagnetic layer and the ferromagnetic layer (1). For this reason, the ferromagnetic layer (1) is also referred to as a magnetic pinned layer.
As mentioned above, the CPP-type element that is configured with a connection between a shield layer and an MR element through a metal is advantageous because it increases heat dissipation efficiency and operating current. In this CPP element, a smaller cross sectional area of an element has a larger resistance value and a larger resistance variation. Namely, it is an appropriate structure for a so called narrower track width. A narrower track width increases the number of tracks per inch (TPI), and it is an essential technology for increasing the recording density of a hard disk drive (HDD).
Examples of the reading element in the CPP-type structure are as follows: a tunneling magnetoresistance (TMR) element with an insulating material as a spacer layer, such as MgO or Al2O3; a CPP-GMR element with a conductive material of a semiconductor, such as Cu, Au, or Ag; and a current confined path (CCP) CPP-GMR element in which a current path configured with a nonmagnetic metal in an insulating layer.
With respect to a signal to noise (S/N) ratio that is an important parameter in the reading element mentioned above, an MR ratio contributes to the signal portion of the S/N ratio, and element resistance contributes to the noise portion of the S/N ratio, respectively. In short, a low resistance element having a higher MR ratio is strongly sought. This demand is applicable to any type of reading elements discussed above. A proposition of a configuration for a novel element having a higher MR ratio in the same element resistance is sought.
CoFe is generally used for two magnetic layers that sandwich a spacer layer, which is a part of a primary structure generating a magnetoresistive effect (MR effect). When a content ratio of Fe in CoFe is higher, an MR ratio of an element has the tendency to be higher. The content ratio of Fe in CoFe is usually approximate 70% by atomic weight.
According to a phase diagram of Co—Fe shown in FIG. 14 (BINARY ALLOY PHASE DIAGRAMS 2ND edition, T. B. Massalski), when Fe was added with approximately 23% by atomic weight or higher, the CoFe is generally formed in an αFe phase at a temperature from an ordinary temperature to 500° C., which was a typical temperature range of manufacturing and operating for a thin film magnetic head. Note that, even though FIG. 14 does not show data below 500° C., when the CoFe is in an αFe phase at a temperature of 500° C., a state of the CoFe is supported as an αFe phase at a temperature range below 500° C. A crystal structure of this αFe phase was configured with a body centered cubic (bcc) structure and was generally oriented in a (110) plane at a temperature of a laminating process.